Clean drinking water for everyone

It’s easy enough to purify clear water. The solar water disinfection method, or SODIS, calls for leaving a transparent plastic bottle of clear water out in the sun for six hours. That allows heat and ultraviolet radiation to wipe out most pathogens that cause diarrhea, a malady that kills 4,000 children a day in Africa.

It’s a different story if the water is murky, as it often is where people must fetch water from rivers, streams and boreholes. “In the developing world, many people don’t have access to clear water, and it’s very hard to get rid of the suspended clay particles,” says Joshua Pearce, an associate professor of materials science and engineering. “But if you don’t, SODIS doesn’t work. The microorganisms hide under the clay and avoid the UV.”